1. Field of the Invention
The present invention relates to a laminated ceramic electronic component such as a laminated capacitor and laminated varistor and, more specifically, to a laminated ceramic electronic component in which the electrode structure is improved.
2. Description of the Related Art
FIG. 3 is a vertical cross section showing one example of a conventional laminated capacitor.
The laminated capacitor 51 comprises a ceramic sintered body 52 constructed of a dielectric ceramic. A plurality of inner electrodes 53 to 56 are disposed in the laminated capacitor 51 so as to be stacked one on top of the other along the direction of thickness via respective ceramic layers. The inner electrodes 53 and 55 extend to one end face 52a of the ceramic sintered body 52, while the inner electrodes 54 and 56 extend to the opposite end face 52b. Outer electrodes 57 and 58 are formed so as to cover the end faces 52a and 52b, respectively.
The outer electrodes 57 and 58 of the laminated capacitor 51 include electrode cover members 57a and 58a which cover the upper face 52c and lower face 52d in order to be mounted on the surface of a printed circuit board.
The length of the electrode cover members 57a, 58a as measured along the direction between the end faces 52a and 52b, is as short as possible to achieve miniaturization of the laminated capacitor 51. As a result, the distance e between the inner side edge of the electrode cover members 57a, 58a and the outermost side edge of the electrodes 57, 58 are made to be relatively small in the conventional laminated capacitor 51. In the outer electrode 58, for example, the distance e is 1 to 1.5 times as long as Lg (the distance between the tips 53a and 55a of the inner electrodes 53 and 55, respectively, and the outer most side edge of the outer electrode 58). A similar relationship exists on left hand side of the capacitor.
When the laminated capacitor 51 is packaged on the printed circuit board by soldering, a heat pulse is applied to the laminated capacitor 51. In response to this heat pulse, the outer electrodes 57 and 58 and the inner electrodes 53 to 56 in the laminated capacitor 51 are more likely to contract than the ceramic material. This contraction stress tends to concentrate at the inner side edges of the cover members 57a and 58a of the outer electrodes 57 and 58, for example at the location indicated by arrow B in FIG. 3. Also, the heat pulse stress is readily concentrated at the tip portions of the inner electrodes 53 to 56 located within the ceramic sintered body 52. Accordingly, cracks are sometimes generated between the site indicated by the arrow B and the tip 53a of the inner electrodes 53.
When the printed circuit board suffers a temperature variation or is bent after the laminated ceramic capacitor has been mounted on the printed circuit, cracks as described above are liable to occur by a stress ascribed to bending or heat impact applied to the ceramic sintered body 52.
The distances e and Lg tend to be shorter as the laminated capacitor is miniaturized. Consequently, these cracks tend to be generated more frequently since the site indicated by the arrow B comes closer to the tip 53a of the inner electrode 53.